The most shocking feature of China's new J-31 stealth fighter, which resembles a F-22 Raptor (e.g. America's premier stealth fighter) with integrated DSI (diverterless supersonic inlet), is the twin engines.

Are the twin engines designed to provide supercruise capability for the J-31? If so, the Chinese J-31 is clearly superior to the supercruise-incapable American F-35 in this critical flight performance.

"China's New Stealth Fighter. Not a repeat from December 2010.
Posted by Bill Sweetman 11:38 AM on Sep 16, 2012

The US defense secretary is on his way to Beijing. Time to unveil a new stealth fighter...

Short take-off and vertical landing has been one of the two driving requirements behind the Joint Strike Fighter design, the other being stealth.

STOVL dictated the single engine, and the STOVL solution chosen for the F-35 demands a big vertical bay behind the cockpit, and a main engine located unusually far forward, to keep the driveshaft length within reason and to put the lift-cruise nozzle in the right longitudinal location for balance.

This constrains the weapon-bay volume and effectively subdivides the bays into four zones - two AAM bays and two heavy store sections. As Amy Butler reports in Aviation Week this week, too, the weapon bays, wrapped around the engine, get hot.

If you ever wondered what a JSF might look without those constraints, we now have a live, physical example.

Unfortunately...

..it's Chinese.

One of the photos of the new Shenyang stealth fighter, apparently designated J-31, that appeared on Chinese defense websites over the weekend is such a colossal gimme that it has to have been deliberate. Direct head-on shot? Check. Commercially available aircraft tug? Check. Extreme telephoto, so that perspective effects are lost in the noise? Check.

Sheesh, guys, can't you make it a challenge?

The J-31's wingspan is an F-35-like 37.5 feet, unless my Soviet-watching skills have deserted me. This makes it smaller than the F-22 and considerably smaller than the Chengdu J-20. A good early guess is that the engines are Klimov RD-93s - imported in large numbers for the JF-17 - with a Chinese-built engine to follow.

Turning to the side view of the jet, it looks as if the engines are installed to the rear of the bulkhead that carries the main landing gears. And with no lift fan bay to worry about, the designers have been able to install long weapon bays on the centerline: what will be interesting is how the inlet ducts are routed to optimize internal space.

Overall, the most important point is that the J-31 does not look like a competitor for the J-20 - but as a complement to it.

And if you wonder about the detail similarities of the shape to the F-22 and F-35, remember this quote from 2010:

In the past year (2009) alone, Lockheed Martin found “six to eight companies” among its subcontractors “had been totally compromised – emails, their networks, everything” according to Lockheed Martin chief information security officer Anne Mullins."

[Note: You should ignore the last paragraph in the article. It is an unproven allegation. There is no proof that China was involved in any way. It could easily have been a Western hacker, such as another Gary McKinnon.

"McKinnon is accused of hacking into 97 United States military and NASA computers over a 13-month period between February 2001 and March 2002, using the name 'Solo'.[2]

The US authorities claim he deleted critical files from operating systems, which shut down the US Army’s Military District of Washington network of 2,000 computers for 24 hours. McKinnon also posted a notice on the military's website: 'Your security is crap'."]

A second Chinese stealth fighter, apparently from Avic’s Shenyang plant, has appeared in seemingly genuine pictures that cropped up on Chinese web sites Sept. 15.

The twin-engine, single-seat fighter, shown at an airfield, appears to approximate the Lockheed Martin F-35 in size, with a somewhat shallower body but a similar span of about 11.4 meters (37.5 ft.), as indicated by comparison with a commercial aircraft tug shown pulling it.

The aircraft features a large ventral weapons bay. Wing sweep looks to be less than 45 deg. on the leading edge, as it was on a wrapped fighter-like object that was hauled by road from Shenyang to Xi’an in June. That trucked object could well have been the now-assembled prototype, three photographs of which have appeared.

Whenever photographs of new weapons appear on nonofficial web sites in China, the risk of fakery is at least as great as elsewhere. But the publication and sustained appearance of the three shots on the large Chinese web portal Sina somewhat supports their veracity.

The source of the pictures is unknown; assuming they are real, they are probably official but unacknowledged, intended to let the world know how far China has gone in developing a smaller companion to the so-called J-20 fighter of Chengdu Aircraft, Shenyang’s rival.

Moreover, the photographs have evidently been staged with the intent of not only revealing the fighter but also letting observers easily measure it and appreciate some of its features. The object hauled on the back of a truck in June was similarly placed next to objects of known size to aid photometric analysis.

Among the most distinctive features on the prototype are doors for the weapons bay. They were about a third as long as the whole aircraft, meaning that the bay must be at least 5 meters long. Assuming that the Chinese military has deliberately revealed the prototype, it surely opened the doors just as deliberately, to show the location and size of the bay. Similarly, a directly head-on shot conveniently showed trapezoidal intakes much like the F-22’s and the angle of the twin canted fins and lower body, about 25 deg.

The engines could well be Klimov RD-93s, which have been imported from Russia for the JF-17 export fighter. If so, a Chinese engine would presumably follow. The engines appear to be installed aft of the bulkhead that carries the main landing gear. The exact routing of inlet ducts, a key issue in reducing radar reflections, could not be judged, but a bulge on top of the fuselage shows that they rise well above the wing.

The location of the prototype was not clear from the photos, but Xi’an, the destination of the trucked object in June, has a flight test center. While China has not officially acknowledged the existence of the Shenyang aircraft, it has been popularly called J-21 or J-31. Shenyang displayed a model of a similar aircraft labeled F-60 last year. The prototype differs at least in having different moveable wing surfaces and in lacking a stinger between the nozzles.

Simultaneous development of two stealth fighters indicates the allocation of enormous resources by China. But if the country is to continue to catch up to Western fighter technology, it probably cannot afford first to get the J-20 into service and then to move on to a smaller aircraft as a replacement for Chengdu’s J-10. The J-10 began large-scale entry into service in 2006 and is unlikely to be considered fit as a first-rank aircraft in the late 2020s.

Also, China will want a domestically built fighter for the aircraft carrier it is now testing, as well as any follow-on ships. The J-20 is probably too large for carrier use. On the other hand, views of the truck-hauled object suggested that the Shenyang fighter had only a modestly sized wing; carrier aircraft need relatively large wings. Conceivably, a big-wing carrier version of the new fighter could be built, like the F-35C."

I said the Chinese J-31/F-60 stealth fighter has twin engines, because supercruise capability was probably part of its design specifications. On the other hand, the single-engine American F-35 was originally designed to be a "bomb truck" and supercruise was never seriously considered.

The alternative theory (for the twin engines on the J-31/F-60) proposed by American experts is the possible lack of confidence in a single-engine fighter. They raise the usual anti-China propaganda about potential unreliability of Chinese engines.

It is easy to prove that the American experts are wrong. China's J-10A and J-10B Vigorous Dragon fighters are equipped with only a SINGLE Chinese WS-10A engine. Therefore, if China wanted to follow the F-35 route then it could have easily built a single-engine J-31/F-60.

However, China intentionally designed a twin-engine J-31/F-60. I think my theory of a supercruise-capable J-31/F-60 is the best explanation. The reason is obvious. China will eventually build thousands of J-31/F-60 stealth fighters with superior performance to defeat supercruise-incapable F-35s. China's strategic goal is to dominate the air against any challenger.

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Citation for faulty American expert analysis of J-31/F-60.

In my view, Andrew Erickson and Gabe Collins show their lack of knowledge regarding single-engine Chinese J-10A and J-10B fighters with a domestic WS-10A engine.

"Alternatively, the J-31’s twin-engine design could also reflect design inefficiencies that would increase the net weight as compared to U.S. airframes of similar size or even lack of trust in the reliability of engines currently available. A single-engine design such as the F-35 for naval operations implies an extremely high degree of confidence in engine reliability."

Could the WS-10A engine power the J-10, J-11B, and J-15 aircraft? The answer is "yes" if two conditions are met. Firstly, Chinese production of WS-10A engines must be sufficient to meet the demand (including production of parts for maintenance and replacement engines at the end of the expected lifetime) for all three aircraft.

Secondly, I don't know if WS-10A engines are interchangeable with AL-31F engines. If they are not readily interchangeable without modifying the fuselage then the current fighters with AL-31F engines will most likely stay with AL-31F replacement engines.

J-10B Vigorous Dragon flying with WS-10A engine

J-11B flying with WS-10A engines

J-15 Flying Shark with WS-10A engines

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WS-10A engine for J-10B Vigorous Dragon fighter in mass production

WS-10A engine (with gearbox at the bottom) is designed to power the J-10B Vigorous Dragon fighter. This version of the WS-10A turbofan engine is said to have 13.2 ton maximum thrust. There are several wrapped engines near the floor.

On Oct. 31 at 10:32 AM, China’s second fifth-generation J-31 stealth fighter successfully took off from AVIC SAC (Shenyang Aircraft Corporation) test flight center and completed its trial flight; accompanied by one J-11BS fighter. The test pilot is Li Guoen (李国恩), who is also the test pilot for the SAC J-15 and J-16 fighters.

The flight duration time was about 10 minutes. At 10:41 AM, the J-31 landed and returned to base. Some senior AVIC officials and PLA Air Force commanders may have observed the test demonstration. Some reports indicate that it only took SAC 19 months to realize the trial flight from aircraft design completion, under competitive pressure from the CAC J-20 stealth fighter.